Traditional mixed active builder containing slurries utilize water as the carrier system for both the active (e.g. surfactant) and solids (e.g. builders such as zeolite, carbonate, and the like). This usually results in high slurry moisture content (i.e. 40-50%).
Liquid active mixtures on the other hand allow for water and active together to act as a carrier for the solids. The active has changed its function in the slurry. The active instead of being a "solid additive" which must be suspended in the liquid water carrier has itself become part of the liquid carrier system. This change allows for a reduction in the amount of water needed in the slurry as a carrier, because the active substitutes for part of the water.
In the spray-drying process there are frequently opposing factors; for example, more water present in a slurry, requires more evaporation, with a resultant increase in costs. If less water is used to save costs, the slurry becomes correspondingly more viscous until a point is reached at which it cannot be pumped and metered. An additional factor, due to market considerations is that the finished product requires higher quantities of surfactant. Spray-drying, for example, increased quantities and certain types of nonionic surfactant lead to pluming from the spray tower. High temperatures contribute to this pluming. Generally other things being equal, spray-drying of a slurry having a lower water content leads to less heat input in the tower than high water content. It is thus desirable to be able to spray-dry low water content slurries while minimizing the problem of high slurry viscosity. A further advantage is that high density powders may be thus obtained.
U.S. Pat. No. 4,738,793 employs low moisture slurries for spray-drying but this is accomplished using nonionic surfactants in the substantial absence of anionic surfactant (less than 2% anionic is taught).
The current art describes the use of high shear mechanical devices to achieve high powder density (&gt;600 g/L) with zeolite layering to control particle size distribution of the final product U.S. Pat. No. 4,869,843. Also described is use of nonionic surfactant sprayed onto base powder with addition of secondary materials to achieve high powder density (&gt;450 g/L). U.S. Pat. No. 5,030,379 to Knight et al.
The methods employed by the art for lowering slurry moisture and avoiding pluming from high temperatures or high nonionic concentrations have not been completely satisfactory.